Hi Paul, On Wed, Jan 24, 2018 at 03:02:58PM +1100, Paul Mackerras wrote: > On Thu, Jan 11, 2018 at 06:11:38PM +0800, wei.guo.simon@xxxxxxxxx wrote: > > From: Simon Guo <wei.guo.simon@xxxxxxxxx> > > > > Currently guest kernel doesn't handle TAR fac unavailable and it always > > runs with TAR bit on. PR KVM will lazily enable TAR. TAR is not a > > frequent-use reg and it is not included in SVCPU struct. > > > > To make it work for transaction memory at PR KVM: > > 1). Flush/giveup TAR at kvmppc_save_tm_pr(). > > 2) If we are receiving a TAR fac unavail exception inside a transaction, > > the checkpointed TAR might be a TAR value from another process. So we need > > treclaim the transaction, then load the desired TAR value into reg, and > > perform trecheckpoint. > > 3) Load TAR facility at kvmppc_restore_tm_pr() when TM active. > > The reason we always loads TAR when restoring TM is that: > > If we don't do this way, when there is a TAR fac unavailable exception > > during TM active: > > case 1: it is the 1st TAR fac unavail exception after tbegin. > > vcpu->arch.tar should be reloaded as checkpoint tar val. > > case 2: it is the 2nd or later TAR fac unavail exception after tbegin. > > vcpu->arch.tar_tm should be reloaded as checkpoint tar val. > > There will be unnecessary difficulty to handle the above 2 cases. > > > > at the end of emulating treclaim., the correct TAR val need to be loaded > > into reg if FSCR_TAR bit is on. > > at the beginning of emulating trechkpt., TAR needs to be flushed so that > > the right tar val can be copy into tar_tm. > > Would it be simpler always to load up TAR when guest_MSR[TM] is 1? > > Paul. Sure. it will have a similar solution with math regs. Thanks for the suggestion, BR - Simon
